Transmitters don't necessarily need to have a FIFO managed buffer
for their transfers.

When registering the driver, before allocating the buffer, check
whether the device is a transmitter or receiver. Allocate the
buffer only for receivers.
Signed-off-by: Andi Shyti <andi.shyti@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>